Localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS) studies of 4-aminothiophenol adsorption on gold nanorods

In the present work, we study the adsorption of p-aminothiophenol (p-ATP) on gold nanorods (GNRs) using localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS) spectroscopies, as function of molecular concentration and pH values in solution. The LSPR spectra reveal the adsorption of p-ATP molecules onto the ends of GNRs. We address the intriguing case that has recently emerged in SERS literature regarding the interpretation of p-ATP SERS spectrum. Apart from typical electromagnetic bands of p-ATP, the aggregation of GNRs at basic pH revealed the appearance in SERS spectra of some extra bands, which can be assigned to the formation of p,p′-dimercaptoazobenzene (DMAB) through chemical transformation of p-ATP on metallic substrates. We correlate the SERS results with theoretical simulations of electromagnetic enhancement of Raman signal for individual and assembled GNRs by employing the Finite-Difference Time-Domain (FDTD) method.